The recent proliferation of portable, battery-powered electronic communication devices has increased the need for low voltage, low on-resistance power MOSFETs for efficient power management. For low voltage MOSFETs, the channel resistance is a large component of the overall on-resistance. Therefore lowering the channel resistance results in a corresponding reduction in on-resistance.
FIG. 1 schematically depicts a prior art device 100 having a planar DMOS stripe configuration on a substrate 101 having a doped upper layer 102. Upper layer 102 includes doped P-well regions 103 and heavily doped N+ source regions 104. On an upper surface 105 of upper layer 102 is a gate region 106 that includes an insulating layer 107 and a conductive layer 108.
One means for reducing channel resistance in a prior art device such as 100 is to increase its channel density in the region 109 of layer 102 underlying gate region 106. Increasing channel density, however, would require a reduction in device geometry and/or a process modification that may be subject to equipment and technique limitations. The present invention offers a desirable alternative to the increased channel density approach for achieving reduced on-resistance in a power device.